What is the fixed fee method?

Excuse me, could you please clarify what the fixed fee method entails in the context of cryptocurrency and finance? Is it a specific pricing strategy adopted by exchanges or service providers, where a predetermined amount is charged for a particular transaction or service, regardless of its size or complexity? I'm curious to understand its advantages and potential drawbacks, as well as how it differs from other fee structures commonly used in the industry. Thank you in advance for your explanation.